U.S. Pat. No. 4,921,767, issued to Datta et al., on May 1, 1990, describes the basic method of manufacturing a luminescent screen for a color CRT by an electrophotographic screening (EPS) process, using dry-powdered, triboelectrically-charged screen structure materials that are serially deposited onto a suitable photoreceptor disposed on an interior surface of a faceplate panel. The photoreceptor comprises, preferably, an organic conductive (OC) layer and an overlying OPC layer. U.S. Pat. No. 5,083,959, issued to Datta et al., on Jan. 28, 1992, describes an apparatus for charging the OPC layer of the photoreceptor formed on the interior concave surface of the viewing faceplate. The apparatus includes a corona generator and at least one corona charger having an arcuately shaped charging electrode which is attached to a support arm that is pivotally attached to the apparatus, at a center of curvature of the faceplate panel. The corona charger swings in an arc across the concave interior surface of the faceplate panel to charge the OPC layer, in about 30 to 60 seconds. The relatively long charging time is not a problem in a laboratory environment; however, such a long charging time is incompatible with efficient commercial production, where each step in the EPS process should, ideally, take about 8 to 10 seconds. It is therefore desirable to increase the charging speed by a factor of about three or four, without jeopardizing the uniformity of the charge applied to the OPC layer, or without adding additional charging devices that would increase the manufacturing cost of the CRT.
Applicants have determined that it is not possible to increase the arcuate speed of the charger described in U.S. Pat. No. 5,083,959 without inducing nonuniform charging of the OPC layer. Accordingly, an apparatus utilizing a corona charger having a different configuration is required to obtain the charging speed necessary for commercialization of the EPS process.